The hydroformylation of an olefinic compound with carbon monoxide and hydrogen to produce aldehydes using an organic solubilized rhodium-phosphorus ligand complex catalyst is well known in the art.
For the most part such prior art methods have involved the non-aqueous hydroformylation of an olefin using rhodium-phosphorus ligand complex catalysts wherein the phosphorus ligand is an organophosphine or organophosphite free of an ionic charge, e.g., simple triphenylphosphine. However, while such processes have been very effective in hydroformylating low molecular weight olefins, their use has been found to be curtailed somewhat when hydroformylating high molecular weight olefins due to the difficulty in separating the higher boiling aldehyde products from the rhodium-phosphorus complex containing reaction product composition.
It has been proposed to use aqueous solutions of sulfonated aryl phosphine compounds as the phosphorus ligand, such as the sulfonated triphenylphosphine salts disclosed e.g., in EPC 163234 and U.S. Pat. Nos. 4,248802, 4,399,312, and the like, as the phosphorus ligand in an aqueous hydroformylation process to facilitate the separation and recovery of the rhodium-phosphorus complex. However, all such prior art methods also involve the employment of a large amount of water to establish a two-phase liquid, non-homogenous hydroformylation reaction medium made up of both an organic phase containing the reaction starting materials and products and an aqueous or water phase containing the catalyst complex and sulfonated phosphine ligands. Moreover, such aqueous or water phase type hydroformylation systems in general require high reactor pressures and/or high metal catalyst concentrations to overcome intrinsically low hydroformylation reaction rates and/or the use of larger and more costly processing apparatus equipment.
It has further been proposed to hydroformylate olefins in a non-aqueous manner employing ionically charged phosphorus ligands and a rhodium-phosphorus ligand complex catalyst such as disclosed e.g., in assignee's U.S. Pat. Nos. 4,731,486 and 4,633,021. However, said U.S. Pat. No. 4,731,486 advocates the use of distillation to separate and recover the aldehyde product, while U.S. Pat. No. 4,633,021 promotes recovery of the aldehyde by extraction with a hydrocarbon solvent and both methods have certain drawbacks. For instance, the higher the molecular weight of the aldehyde product the more difficult distillation becomes due to the higher temperatures required. Moreover, extraction with a hydrocarbon alone is not considered to be a very efficient separation method, since it has been found to extract substantial amounts of the rhodium-phosphorus complex and/or free phosphorus ligand and/or the organic solubilizing agent for said complex and said free ligand that are also present in the reaction product composition in addition to extracting the aldehyde product.
Therefore, there remains a need in the hydroformylation art for a more effective and simple method for efficiently separating higher molecular weight aldehyde products from such non-aqueous hydroformylation reaction product compositions.